1. Field of the Invention
The present invention relates to a photoelectric conversion substrate, a photoelectric converter, a radiographic imaging substrate, and a radiographic imaging apparatus applied to a medical diagnostic imaging system, a non-destructive inspection device, a radiographic analyzer, or the like. It is assumed in this specification that radiation includes electromagnetic waves including visible light, X-rays, and gamma rays, as well as alpha and beta radiation.
2. Description of the Related Art
As a conventional typical radiographic imaging apparatus, there is a radiographic imaging apparatus constructed of a combination of a radiographic imaging substrate, on which there are arranged optical sensors of MIS-TFT structure each formed of an MIS-type photoelectric conversion element and a switching TFT, and phosphors for converting radiation to visible light. This type of radiographic imaging apparatus is disclosed in U.S. Pat. No. 6,075,256.
FIGS. 13, 14, and 15 show a schematic diagram, an equivalent circuit diagram, and a plan view of a conventional radiographic imaging apparatus, respectively. FIGS. 16 and 17 show a cross section of a single pixel and an enlarged view of a portion close to a cut section of the radiographic imaging substrate.
References P11 to P44 designate photoelectric conversion elements or other semiconductor conversion elements and references T11 to T44 designate thin film transistors (TFTs), and each pair of them forms a pixel. While a pixel area 2 of 4×4 pixels is shown here, for example, 1000×2000 pixels are practically arranged on a radiographic imaging substrate (insulating substrate) 1.
As shown in FIGS. 14 and 15, the photoelectric conversion elements P11 to P44 are connected to common bias lines Vs1 to Vs4 and a readout device 5 applies a given bias to them. The respective gate electrodes of the TFTs are connected to common gate lines Vg1 to Vg4 and a gate drive unit makes an ON-OFF control of the TFT gates. Source or drain electrodes of the TFTs are connected to common signal lines Sig1 to Sig4 and Sig1 to Sig4 are connected to the readout device 5.
X-rays emitted to a subject are attenuated by, pass through the subject and are converted to visible light in a phosphor layer 19 arranged via a adhesive layer 18 shown in FIG. 16. Then, the visible light is incident on the photoelectric conversion elements P11 to P44 and converted to electric charges. These charges are transferred to signal lines Sig1 to Sig4 via the TFTs T11 to T44 by means of gate drive pulses applied by a gate drive unit 4 and then read out to the outside by a readout device 5. Thereafter, the common bias lines remove residual charges that have been generated in the photoelectric conversion elements P11 to P44, but have not been transferred.
The conventional radiographic imaging apparatus has a radiographic imaging substrate 1 cut in a cut section indicated by a dashed line in FIG. 17, with the signal lines Sig1 to Sig4 and the bias lines Vs1 to Vs4 connected to the readout device 5 and the gate lines Vg1 to Vg4 connected to the gate drive unit 4 via a printed circuit board such as tape carrier packages (TCPs) 6 and 7, respectively. It is assumed here that TCP-A6 is a TCP connected to the readout device 5 and that TCP-D7 is a TCP connected to the gate drive unit 4.
A layer structure is shown in FIG. 16. An MIS-type photoelectric conversion element is formed of an under electrode (first electrode layer 11), an insulating layer (first insulating layer 12), a photoelectric conversion layer (first semiconductor layer 13), a hole blocking layer (doping semiconductor layer 14), and an upper electrode (second electrode layer 15), with the under electrode (first electrode layer 11) connected to a TFT source-drain electrode (second electrode layer 15). The TFT includes a gate electrode (first electrode layer 11), a gate insulating layer (first insulating layer 12), a semiconductor layer (first semiconductor layer 13), an ohmic contact layer (doping semiconductor layer 14), and a source-drain electrode (second electrode layer 15). Each Vg line and each Sig line are connected to the electrode layer where the TFT gate electrode 11 is formed and to the layer where the source-drain electrode 15 is formed, respectively. Moreover, the photoelectric conversion element and the TFT are coated with and protected by a second insulating layer 16 and an organic protective layer 17. It should be noted here that the first semiconductor layer 13 is formed of an intrinsic semiconductor and that the doping semiconductor layer 14 is formed of an n- or p-type semiconductor to which impurities such as phosphorus or boron have been introduced.